Magnetostatic microwave device having large impedance change at resonance

ABSTRACT

A magnetostatic wave microwave device comprising a thin magnetostatic wave element and a conductor disposed on the top of said magnetostatic wave element. Because the width of an junction portion of the conductor is larger than the width of an input portion of the conductor, a large impedance change of the magnetostatic wave element at resonance can be obtained while maintaining a Q-value at a high level.

BACKGROUND OF THE INVENTION

The present invention relates to a magnetostatic wave microwave deviceutilizing ferrimagnetic resonance and comprising a magnetostatic waveelement and a means for exciting magnetostatic waves, which is used inmany microwave components and in particular is used in oscillators.

Recently, as a magnetostatic wave microwave devices for use in a filter,an oscillator, etc. which utilizes ferrimagnetic resonance of aferrimagnetic thin film, those having a magnetostatic wave element whichis produced by forming a ferrimagnetic YIG (yttrium-iron-garnet) thinfilm on a non-magnetic, single crystalline substrate of GGG(gadolinium-gallium-garnet) by liquid phase epitaxial growth (LPE),etching it by a photolithographic technique and machining the etchedfilm into a desired shape such as circle, rectangle, etc. has beenproposed. These magnetostatic wave microwave devices have advantagebecause they can be made into a microwave integrated circuit using amicrostrip line, etc. as a transmission line, and they can be easilyconnected with other microwave integrated circuits by hybrid junction.

In addition, since a magnetostatic wave element utilizing YIG film canbe produced by LPE and machining, it has a high productivity as comparedwith a conventional magnetostatic wave element utilizing YIG spheres.

However, the performance of a magnetostatic wave microwave deviceutilizing ferrimagnetic resonance of YIG film is significantly dependenton geometric shape of the YIG film. In order to obtain a largeimpedance, a YIG film having a large surface area and large thickness isrequired. However, these large surface area and thickness aredisadvantageous from a view point of miniaturizing microwave circuitsand maintaining a ferrimagnetic resonance of a large Q-value.

Generally, a circuit, as shown in FIG. 15, in which an LC parallelresonator of concentrated-constant type is connected at a distance dfrom an input terminal T is an ideal equivalent circuit formagnetostatic wave microwave devices. In order to obtain a largeimpedance change, the length of the magnetostatic wave element along thepropagation direction of microwave has been made longer in the priorart. In this method, however, the length L of the magnetostatic waveelement becomes comparable to the wavelength of microwave so that theequivalent circuit in this case is expressed by a distributed constantcircuit, as shown in FIG. 16, in which an indefinite number of LCresonators are connected along the direction of L. This corresponds toobserving simultaneously a plurality of resonators excited by microwavesof different phases, resulting in failure to obtain a high Q-value ofthe magnetostatic wave element.

On the other hand, when the length L, width W and thickness t of themagnetostatic wave element are simultaneously made smaller in order toobtain a high Q-value, although a higher Q-value can be obtained, themagnetostatic wave element absorbs very little energy from a microwave.This means that the impedance change at resonance is significantlyreduced.

FIG. 12 is a schematic view showing a conventional magnetostatic wavemicrowave device utilizing a rectangular YIG film. A rectangular, thinmagnetostatic wave element 1 is disposed between a ground conductor 3and a microstrip line 2 which is shorted at the end thereof. An externalmagnetic field Hext for causing ferrimagnetic resonance is appliedperpendicularly to the surface of the magnetostatic wave element 1.Microwaves propagate along the direction of an arrow 4a and arereflected in the direction of an arrow 4b. The reference character Wimeans the width of the microstrip and the reference character d meansthe distance between the edge of the microstrip line 2 and the nearestedge of the magnetostatic wave element 1. In the conventional device,the length L and the width W of the magnetostatic wave element 1 arenearly the same, i.e., the upper surface of the magnetostatic waveelement 1 is nearly square. In the prior art, in order to obtain alarger impedance change at resonance measured from the input portion ofthe microstrip line, L, W and t of the magnetostatic wave element 1 havebeen simultaneously made longer. However, as mentioned above, increasedL, W and t result in reduction of the Q-value of the magnetostatic waveelement 1. In contrast, decreased L, W and t lead to reduction of theimpedance change at resonance.

FIG. 13 is a schematic view showing a conventional magnetostatic wavemicrowave device utilizing a circular YIG film. In the conventionalmagnetostatic wave microwave device, when the outer diameter D and thethickness t of the magnetostatic wave element 1 are made larger in orderto obtain a large impedance change at resonance, the Q-value of themagnetostatic wave element 1 is reduced. When D and t are made smallerfor obtaining a high Q-value, the impedance change at resonance isreduced.

FIG. 14 is a schematic view showing a conventional magnetostatic wavemicrowave device having an electrode finger structure 7. Thismagnetostatic wave microwave device also has the same disadvantages asthose in the magnetostatic wave microwave device shown in FIGS. 12 and13. Namely, when the length L and the thickness t of the magnetostaticwave element 1 are made larger in order to obtain a large impedancechange at resonance, the Q-value of the magnetostatic wave element 1 isreduced. On the other hand, when the length L and the thickness t aremade smaller for obtaining a high Q-value, the impedance change atresonance is reduced.

FIG. 17 is a schematic illustration showing a magnetostatic wavemicrowave device in which a right end-shorted microstrip line 2 isdisposed with a magnetostatic wave element 1 at a short portion. A waveI with hatched lines shows a standing wave of a microwave current. Themicrowave current has the maximum magnitude at the short portion. Thereference numeral 3 is a ground conductor.

In this device, a larger impedance change of the magnetostatic waveelement 1 at resonance can be attained by elongating the sides of therectangular magnetostatic wave element 1 along the propagation directionof microwave (FIG. 18). The disadvantage in this method has beendescribed above by referring to FIG. 16.

Alternative method for attaining a larger impedance change is toincrease the thickness of the magnetostatic wave element 1 (FIG. 19).However, the shape of the magnetostatic wave element 1 is unfavorablydeformed from flat spheroid which is regarded as an ideal shape for themagnetostatic wave element 1, thereby resulting in a significantlyreduced Q-value of resonance characteristics.

Still another method for attaining a larger impedance change is to makethe width (perpendicular to the propagation direction of microwave) ofthe magnetostatic wave element 1 longer than the length (along thepropagation direction of microwave) of the magnetostatic wave element 1(FIG. 20). However, a greater part of the magnetostatic wave element 1comes to deviate from the center line of the microstrip line 2 withincreasing width so that the coupling between microwave and themagnetostatic wave element 1 is not necessarily sufficient.

OBJECT AND SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide amagnetostatic wave microwave device which can realize a large impedancechange at resonance while maintaining a Q-value of a magnetostatic waveelement at a high level.

As a result of intense research in view of the above object, theinventors have found that a large impedance change of a magnetostaticwave element at resonance can be attained while maintaining a Q-value ata high level by disposing on a magnetostatic wave element a conductorconsisting of a junction portion, a short portion and an input portion,the widths of the junction portion and short portion being larger thanthat of the input portion. The present invention has been accomplishedbased on this finding.

The finding by the inventors will be explained more in detail referringto FIG. 21. In order to remove the disadvantage in the prior art (FIGS.18-20), the width of the junction portion 2b of the conductor on themagnetostatic wave element 1 is selected to be much longer than that ofthe microstrip line 2. The short portion 2c of the conductor is alsoselected to be much longer than that of the microstrip line 2. With thisstructure, the microwave current concentrated in the center line of themicrostrip line 2 can be widely distributed to interact with the overallportion of the magnetostatic wave element 1. As a result, the couplingbetween microwave and the magnetostatic wave element 1 can be increasedwithout a large shift of microwave phase. Further, in a microwavecircuit of such structure, a magnetostatic wave element can be regardedas a concentrated constant element throughout a wide frequency range.Therefore, a magnetostatic wave element of a large volume can be usedfor attaining a large impedance change at resonance while maintaining aQ-value at a high level.

Thus, in an aspect of the present invention, there is provided amagnetostatic wave microwave device comprising a thin magnetostatic waveelement and a conductor disposed on the top of said magnetostatic waveelement, wherein the conductor consists of an input portion throughwhich microwaves are input, a junction portion at which the conductor isconnected to the magnetostatic wave element, and a short portion to beconnected to a ground conductor, and wherein each of the input portion,junction portion and short portion has a width perpendicular to apropagation direction of said microwaves and the width of the junctionportion is larger than the width of the input portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an embodiment of the presentinvention;

FIG. 2 is a schematic view showing another embodiment of the presentinvention;

FIG. 3 is a schematic view showing another embodiment of the presentinvention;

FIG. 4 is a schematic view showing another embodiment of the presentinvention;

FIG. 5 is a schematic view showing another embodiment of the presentinvention;

FIG. 6 is a schematic view showing another embodiment of the presentinvention;

FIG. 7 is a schematic view showing another embodiment of the presentinvention;

FIG. 8 is a schematic view showing another embodiment of the presentinvention;

FIG. 9 is a cross-sectional view of another embodiment of the presentinvention;

FIG. 10 is a cross-sectional view of another embodiment of the presentinvention;

FIG. 11 is a cross-sectional view of another embodiment of the presentinvention;

FIG. 12 is a schematic view showing a conventional magnetostatic wavemicrowave device;

FIG. 13 is a schematic view showing an another conventionalmagnetostatic wave microwave device;

FIG. 14 is a schematic view showing an another conventionalmagnetostatic wave microwave device;

FIG. 15 is a circuit diagram showing an equivalent circuit of amagnetostatic wave microwave device;

FIG. 16 is a circuit diagram showing an equivalent circuit of anothermagnetostatic wave microwave device;

FIG. 17 is a schematic illustration showing a concept of the prior art;

FIG. 18 is a schematic illustration showing a concept of the prior art;

FIG. 19 is a schematic illustration showing a concept of the prior art;

FIG. 20 is a schematic illustration showing a concept of the prior art;and

FIG. 21 is a schematic illustration showing a concept of the presentinvention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic view showing the basic concept of the presentinvention. In FIG. 1, a rectangular, thin magnetostatic wave element 1having a thickness t of the order of 300-700 μm consists of a GGGsubstrate 1a and a YIG film 1b on the top of the GGG substrate 1a. Thethickness of the YIG film is preferably 10-100 μm. The referencecharacter L means the length, in the order of 0.2-2 mm, of themagnetostatic wave element 1 along the propagation direction ofmicrowave, and W means the width, in the order of 1-5 mm, perpendicularto the propagation direction, of the magnetostatic wave element 1. Aconductor 2 having a thickness of the order of 1-5 μm and located on themagnetostatic wave element 1 consists of an input portion 2a, a junctionportion 2b and a short portion 2c. The input portion 2a, the junctionportion 2b and the short portion 2c have a width Wi of the order of0.3-2 mm, a width Wo of the order of 1-5 mm and a width Wo',respectively. The reference numeral 4a means the propagation directionof microwave or the direction of microwave current in the conductor 2.The reference numeral 3 is a ground conductor 3 and the referencenumeral 4b means the reflection direction of microwave or the directionof microwave current in the ground conductor 3. The directions 4a and 4bare reversed so that the circuit oscillates. An external magnetic fieldHext is applied to the magnetostatic wave element 1 perpendicularly tothe surface of the magnetostatic wave element 1 so that ferrimagneticresonance is caused.

As seen from FIG. 1, in the present invention, the width Wo of thejunction portion 2b is much longer than the width Wi of the inputportion 2a in contrast with the prior art shown in FIG. 12, etc. In theembodiment shown in FIG. 1, the width Wo and the width Wo' of the shortportion 2c are the same. Although the width Wo' may be equal to ornearly equal to the width Wi, it is preferable that the width Wo' isselected to be larger than the width Wi, more preferably to be 1.2-5times the width Wi. The upper surface of the magnetostatic wave element1 is rectangular and its longer side (width W) is perpendicular to thedirection 4a of the microwave current. In this embodiment, the width Woand the length Lo of the junction portion 2b are selected to be equal toW and L.

The structure shown in FIG. 1 makes it possible to increase the couplingbetween the magnetostatic wave element 1 and the junction portion 2b,and to pass microwave to the ground conductor 3 in the electrical lengthsmaller than the length of the short portion 2c because of anelectrostatic capacitance between the junction portion 2b and the groundconductor 3. Therefore, the magnetostatic wave element 1 can be regardedto be nearly a concentrated constant element.

FIG. 2 shows another embodiment of the present invention. The referencecharacters in common with FIG. 1 have the same meanings. In theembodiment of FIG. 2, the width Wo' of the short portion 2c is selectedto be smaller than the width Wo of the junction portion 2b and be nearlyequal to the width Wi of the input portion 2a. Although the width Wo' issmall, the conductor 2 can be regarded to be electrically shorted withthe magnetostatic wave element 1 at the vicinity of the center thereofbecause of a large electrostatic capacitance between the junctionportion 2b and the ground conductor 3. Therefore, the magnetostatic waveelement 1 can be regarded as a concentrated constant element.

FIG. 3 shows another embodiment of the present invention in which themagnetostatic wave element 1 has a dimension larger than that of thejunction portion 2b in both the width and the length. Incidentally,although the magnetostatic wave element 1 consists of a substrate and aferrimagnetic thin film, these are not shown in FIGS. 3-11 for thepurpose of simplification.

FIG. 4 shows another embodiment of the present invention in which thejunction portion 2b has a dimension larger than that of themagnetostatic wave element 1 in both the width and the length.

FIG. 5 shows another embodiment of the present invention in which thewidth of the junction portion 2b become larger as it comes close to theshort portion 2c. The device of this structure can also show the effectof the present invention because the width Wo' is larger than the widthsof the input portion 2a and the junction portion 2b.

FIG. 6 shows another embodiment of the present invention in which thejunction portion 2b and the short portion 2c are separated into twoportions. The device of this structure can also show the effect of thepresent invention as long as the combined width W₁ +W₂ is larger thanthe width Wi.

FIG. 7 shows another embodiment of the present invention in which thejunction portion 2b is formed on the whole upper surface of themagnetostatic wave element 1 by a thin film-forming process such assputtering, vapor deposition, etc. A strip line 10 as the input portionand a conductor 11 as the short portion are respectively connected tothe junction portion 2b. The width Wo of the junction portion 2b is thesame as the width W and is sufficiently larger than the width Wi of thestrip line 10 as the input portion. Also, the width Wo' of the conductor11 as the short portion is selected to be larger than the width Wi. Thedevice of this structure can also show the effect of the presentinvention.

FIG. 8 shows another embodiment of the present invention. In thisembodiment, as is the case in FIG. 7, the junction portion 2b is formedon the upper surface of the magnetostatic wave element 1 by afilm-forming technique such as sputtering, vapor deposition, etc. As theinput portion and the short portion, wire 12a and wires 12b arerespectively connected to the magnetostatic wave element 1 by awire-bonding method. Generally, the surface area of the junction portion2b is larger than the diameter of the wire 12a. For ensuring a completeshort-circuit, the number of the wire 12b is preferred to be larger thanthat of the wire 12a. Incidentally, the short portion may be formed froma wide ribbon by ribbon-bonding method.

FIG. 9 shows a cross-sectional view of another embodiment of the presentinvention. In this embodiment, the short portion 2c is indirectlyconnected to the ground conductor 3 through a capacitor 8 for blockingdirect current which is placed adjacent to the magnetostatic waveelement 1. The reference numeral 5 is a conductor for connecting thecapacitor 8 and the short portion 2c. The device of this structure canalso show the effect of the present invention.

FIG. 10 shows a cross-sectional view of another embodiment of thepresent invention. In this embodiment, the magnetostatic wave element 1is disposed on the capacitor 8 having a comparatively larger surfacearea. The short portion 2c is connected to the conductor 5 as is thecase in FIG. 9. The device of this structure can also show the effect ofthe present invention.

FIG. 11 shows a cross-sectional view of another embodiment of thepresent invention. A strip line 9 is connected to the wide junctionportion 2b at one end and the other end thereof is allowed to be open.The electrical length between the center of the wide magnetostatic waveelement 1 and the open end of the strip line 9 is selected to be 1/4 thewavelength λ of microwave to be used. With this structure, the currentin the junction portion 2b has the maximum value always at the center ofthe junction portion 2b, this state being equivalent to ashort-circuited state. The device of this structure can also show theeffect of the present invention.

What is claimed is:
 1. A magnetostatic wave microwave device comprisinga thin magnetostatic wave element and a conductor disposed on the top ofsaid magnetostatic wave element, wherein said conductor consists of aninput portion through which microwaves are input, a junction portion atwhich said conductor is connected to said magnetostatic wave element,and a short portion to be connected to a ground conductor, and whereineach of said input portion, junction portion and short portion has awidth perpendicular to a propagation direction of said microwaves andthe width of said junction portion is larger than the width of saidinput portion.
 2. The magnetostatic wave microwave device according toclaim 1, wherein the width of said short portion is larger than thewidth of said input portion.
 3. The magnetostatic wave microwave deviceaccording to claim 1, wherein said thin magnetostatic wave element is arectangle with longer sides thereof perpendicular to a propagationdirection of said microwaves.
 4. The magnetostatic wave microwave deviceaccording to claim 1, wherein said conductor is formed in closelycontact with the top of said magnetostatic wave element by a thin-filmforming process.
 5. The magnetostatic wave microwave device according toclaim 1, wherein said short portion is grounded through a capacitor forblocking direct currents.
 6. The magnetostatic wave microwave deviceaccording to claim 1, wherein said magnetostatic wave element comprisesan thin ferrimagnetic film disposed on the top of a substrate.
 7. Themagnetostatic wave microwave device according to claim 1, wherein saidferrimagnetic film mainly comprises yttrium-iron-garnet.